The present invention relates to a washing machine of a type which can automatically correct abnormal conditions which may sometimes occur.
As is well known in the art, in a washing machine the rotary blades of the agitator or pulsator are turned by an electric motor to wash clothes placed in a washing tub of the machine. The motor is usually coupled to the agitator or pulsator through an endless belt.
Sometimes the motor may be forcibly stopped by a external cause, for instance, when an excessively large load is put in the washing machine, or when foreign matter is caught between the tub and the rotary blades, or when a bearing seizes.
If a motor is maintained locked for a long period, it may burn out due to over-heating. This difficulty has heretofore been eliminated by employing a heat-sensitive fuse or a self-restoring type protective unit built into the motor so that, if the motor starts to over-heat, application of current to the motor is suspended.
However, in the case a heat-sensitive fuse is employed, it is necessary to replace the fuse with a new one each time the motor overheats, and in the case of a motor in which a self-restoring type protective unit is incorporated, it is necessary to allow the motor to cool for a long period of time before it can be restarted. Furthermore, the conventional washing machine suffers from the difficulty that the occurrence of an abnormal condition cannot be detected until the motor actually over-heats, as a result of which the motor can eventually suffer breakdown of its electrical insulation.
If the condition of rotation of the rotary blades is detected and the energization of the motor controlled according to the condition of rotation thus detected, then the occurrence of an abnormal condition within the motor can be detected before the motor overheats. Upon elimination of the abnormal condition, the operation of the washing machine can be started again.
In such a washing machine in which the condition of rotation is detected, when an abnormal condition is sensed, the motor, and accordingly the rotary blades, is turned in the opposite direction from that in which it is trying to turn. If turning the motor and the rotary blades in the opposite direction does not eliminate the abnormal condition, the motor is stopped. This method is considerably effective in preventing motor failures in a washing machine.
In a single-tank type fully automatic washing machine, the washing tank (tub) is used also as a dehydrating (spin cycle) tank, and frequently the washing operation is carried out with the lid closed. Therefore, in the case where the motor is stopped as described above, if the operator is not near the machine, it is often difficult to know that the motor has stopped because the amount of noise issuing from the machine is low under normal operating conditions.
In almost all cases where the motor is locked, the cause is an excessively large quantity of clothes put in the machine. When the motor is locked by such a large load, the motor can be readily unlocked, and therefore it is necessary to notify the operator of the locking of the motor quickly; otherwise, the operator may waste a great deal of time.